Automatic keyframing offset?
BlenderDiplom has created an Add-on called AReWo (Animation Replicator with Offset) which does exactly what you want. They provide a Video-Tutorial of how to use it and a Download page where you can find the direct link.

Another possibility is using the Animation Nodes by Jacques Lucke.

Or you can use the Blendgraph Add-on to animate Text with a so called Font Repeater Node.